One known three-way solenoid valve of this kind is shown in FIG. 8 and includes the outer case of a valve portion, a case 1, a rear plate 2, a plunger valve 4 having a plunger 4a, a core 3 for magnetically attracting the plunger 4a, a bobbin 5 made from an insulator, a solenoid coil 6 wound on the bobbin 5 for producing electromotive force, a ball 11, a first valve seat 12 having a seat surface 12a, an input port 13 formed in the case 1 along the axis of the seat 12, an output port 14 formed in the case 1, an exhaust port 15 formed in the case 1, and a second valve seat 16 disposed opposite to the first valve seat 12. The case 1 cooperates with the outer case to form an integrated magnetic circuit. The core 3 is coupled to the rear plate 2 with screws. The first valve seat 12 cooperates with the ball 11 to form a first valve body portion. The second valve seat 16 has a seat surface 16a which cooperates with the ball 11 to form a second valve body portion.
Another solenoid valve has been proposed as disclosed in Japanese Utility Model Laid-Open No. 184278/1988. This valve is shown in FIG. 9 and includes a core 3 having an exhaust port 15, a plunger valve 4 having a communication hole 4c, and a guide member 10 having a communication hole 10a. The exhaust port 15 is located in the uppermost position so that the movable portion of the solenoid valve may be kept immersed in fluid.
In each of the conventional solenoid valves shown in FIGS. 8 and 9, when the coil 6 is not energized, the valve is closed. When the coil 6 is energized, the valve is open. That is, these three-way solenoid valves are normally closed valves.
Therefore, when a normally open three-way solenoid valve is required, it is inevitably different in its entire structure from the normally closed solenoid valve.
In addition, each conventional three-way valve has a case which cooperates with the outer case of the valve portion to form an integrated magnetic circuit and, accordingly, it is cumbersome to assemble the valve. The solenoid device portion and the valve portion are combined in a unit.